HYDROXYCARBOXYLIC ACID PRODUCT

FIELD OF THE INVENTION

The invention relates to the method as de ^¬ fined in the preamble of claim 1 and to the apparatus as defined in the preamble of claim 9 for separating a hydroxycarboxylic acid product from a suspension con ^¬ taining hydroxycarboxylic acid formed as a result of hydrolysis and fermentation of lignocellulose-based raw material. Further, the invention relates to the use of a hydroxycarboxylic acid as defined in the claim 13. BACKGROUND OF THE INVENTION

Hydroxycarboxylic acid based products, e.g. lactic acid, are manufactured from different kinds of lignocellulose-based raw stock, e.g. from waste wa ^¬ ters, residue flows and sludges derived from paper and/or pulp mill. The waste waters contain organic ma ^¬ terial such as fibers and traces of bleaching agents. The process of hydroxycarboxylic acid production is usually based on enzymatic hydrolysis and fermenta ^¬ tion. The produced hydroxycarboxylic acid is separated for example by crystallization.

From WO 9919290 is known a process for the production of lactic acid products from mixture con ^¬ taining free lactic acid and dissolved lactate salt. Preferred mixtures for processing are obtained from fermentation broths, preferably from fermentation processes conducted at a pH of 4.8 or lower. From WO 00/56693 is known a method for purificating lactic ac ^¬ id by distillation and crystallization.

OBJECTIVE OF THE INVENTION The objective of the invention is to disclose a new type of a method and apparatus for separating a hydroxycarboxylic acid product from a suspension con ^¬ taining hydroxycarboxylic acid formed as a result of hydrolysis and fermentation of lignocellulose-based raw material. Further, the objective of the invention is to disclose use of hydroxycarboxylic acid as a con ^¬ centrating agent for increasing the concentration above the eutectic point of the concentration.

SUMMARY OF THE INVENTION

The method for separating a hydroxycarboxylic acid product from a suspension containing hydroxycarboxylic acid formed as a result of hydrolysis and fer- mentation of lignocellulose-based raw material accord ^¬ ing to the present invention is characterized by what is presented in claim 1.

The apparatus for separating a hydroxycarbox ^¬ ylic acid product from a suspension containing hy- droxycarboxylic acid formed as a result of hydrolysis and fermentation of lignocellulose-based raw material according to the present invention is characterized by what is presented in claim 9.

The use of the hydroxycarboxylic acid as a concentrating agent for increasing the concentration of the hydroxycarboxylic acid according to the present in ^¬ vention is characterized by what is presented in claim 13. BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, which are included to provide a further understanding of the invention and constitutes a part of this specification, illus ^¬ trate some embodiments of the invention and together with the description help to explain the principles of the invention. In the figures: Fig. 1 is a flow chart illustration of a method and an apparatus according to one embodiment of the present invention, and

Fig. 2 shows a schematic illustration of an eutectic system of water (A) and carboxyhydroxyl acid (B) .

DETAILED DESCRIPTION OF THE INVENTION

The invention is based on a method for sepa- rating a hydroxycarboxylic acid product from a suspen ^¬ sion containing hydroxycarboxylic acid formed as a re ^¬ sult of hydrolysis and fermentation of lignocellulose- based raw material. According to the invention the suspension containing hydroxycarboxylic acid is treated by a two-stage separation to form the hydroxycarboxylic acid product, the two-stage separation comprising a first separation stage in which water is separated, preferably at least a part of water is removed, from the suspension and a second separation stage in which hy- droxycarboxylic acid product is separated, preferably is concentrated and purified, from the suspension from which water has been removed, and hydroxycarboxylic acid is added to the suspension before the second separation stage, preferably between the first and second separa- tion stages, to increase the concentration of the hy ^¬ droxycarboxylic acid in the second stage.

Further, the invention is based on an apparatus for separating a hydroxycarboxylic acid product 33 from a suspension 31 containing hydroxycarboxylic acid formed as a result of hydrolysis 11 and fermentation 12 of lignocellulose-based raw material 2. According to the invention, the apparatus includes a two-stage sepa ^¬ ration device 36a-b for treating the suspension 31 containing hydroxycarboxylic acid to form the hydroxycar- boxylic acid product 33, and the two-stage separation device comprises a first separation device 36a in which water 37 is separated from the suspension 31 and a se ^¬ cond separation device 36b in which hydroxycarboxylic acid 33 is separated from the suspension 32 from which water has been removed, and a means 39,40 for adding hy- droxycarboxylic acid to the suspension 32 before the se ^¬ cond separation device 36b to increase a concentration of the hydroxycarboxylic acid in the second separation.

Further, the invention is based on an use of hydroxycarboxylic acid as a concentrating agent in a two-stage separation process, e.g. method and/or appa ^¬ ratus, comprising a first stage in which water is re ^¬ moved from the suspension containing hydroxycarboxylic acid and a second stage in which hydroxycarboxylic acid is separated from the suspension containing hydroxycar- boxylic acid and the hydroxycarboxylic acid is led be ^¬ tween the two separation stages of the hydroxycarbox ^¬ ylic acid separation.

The invention is specifically based on the use of at least two-stage separation method for sepa- ration of hydroxycarboxylic acid, e.g. lactic acid, wherein firstly at least a part of water, preferably mainly water, is removed and secondly hydroxycarbox ^¬ ylic acid is concentrated and purified. The eutectical point of the separation, preferably crystallization, is controlled in such a way that the resulting pure hydroxycarboxylic acid is collected in an acid form, not as a salt. Preferably, in the invention there is jumped over the eutectical point after the water crys ^¬ tallization. The new advantage of the invention is that the resulting hydroxycarboxylic acid is pure and ready to be used and no additional purification steps are needed. An additional new feature is that the con ^¬ centration of the hydroxycarboxylic acid in the feed of the hydroxycarboxylic acid purification is in- creased by recycling or by adding pure hydroxycarbox ^¬ ylic acid to the feeding point which is located after the water removing. Then the eutectical point can be exceeded by jumping over it. If at least part of the water is removed and the concentration of the hy- droxycarboxylic acid is high in the hydroxycarboxylic acid separation so then hydroxycarboxylic acid is gen ^¬ erated in the form of acid and a right side of the eu ^¬ tectical point is achieved. Using the hydroxycarbox ^¬ ylic acid formed in the process in the separation, that is, recycling the acid back to the process in- creases also the economy of the process. The eutecti ^¬ cal point is dependent on an effluent, suspension com ^¬ position and concentrations of water and hydroxycarboxylic acid.

In figure 2 is shown a schematic illustration of a eutectic system of water (A) and carboxyhydroxyl acid (B) . In the process of the figure two crystalli ^¬ zation (SMC), e.g. two suspension melt crystallisa ^¬ tion, stages are connected in series. In the first SMC stage (SMC1) the main component in the feed is water, i.e. the hydroxylic acid is present in a very low co- centration. Thus the process operates along the left hand curve depicted as SMC1 in Fig 2. The pure water is crystallised and removed from the system as a solid phase until the process is stopped at a concentration Xw. The concentration Xw is more than 1 % below the concentration in the eutectic point, Xe . At the con ^¬ centration of Xw the uncrystallised fraction of the feed is fed in the second suspension melt crystallisa ^¬ tion unit, SMC2 to increase the concentration of the component B (hydroxylic acid) above the concentration Xe . The starting concentration Xh in SMC2 shown in Fig. 2 is thus more than 1 % higher than Xe . The crys ^¬ tallisation process in SMC2 then follows the curve shown on the right hand side of the eutectic point (Xe) in Fig 1, where the pure hydroxylic acid is crys ^¬ tallised and removed from the system as the solid phase. A part of crystallised acid may liquify when temperature rises. The obtained final purity of the hydroxylic acid is 99 %.

Lignocellulose means in this connection a ma- terial formed from cellulose, hemicellulose and lig- nin. Lignocellulose-based material means in this con ^¬ nection any material containing cellulose and/or hemicellulose, which may also contain, in addition to cel ^¬ lulose and hemicellulose, lignin, starch and/or other substances.

In on embodiment an effluent is used as a raw material. The raw material can includes one or more than one component. In this connection, the term "ef ^¬ fluent" means any effluent selected from the group of pulp mill effluent, paper mill effluent, saw mill ef ^¬ fluent, food manufacturing effluent, brewing industry effluent and their combinations. The effluent compris ^¬ es alkaline and/or acidic waste waters, filtrates and residual waters of the process. In one embodiment the effluent is a waste water, waste sludge or residue flow from the pulp mill. In one embodiment the efflu ^¬ ent is a waste water. In one embodiment the first ef ^¬ fluent can include alkaline and/or acid components, e.g. a bleaching filtrate, and/or any residue effluent which comes from the pulp mill. The effluent contains, at least in some quantity, the lignocellulosic materi ^¬ al described above. The effluent can includes one or more than one component. The raw material can also contain, in addition the effluent, other subtances.

In this invention a hydroxycarboxylic acid can include at least one hydroxycarboxylic acid or combina ^¬ tion of different hydroxycarboxylic acids. In this con ^¬ nection, hydroxycarboxylic acid means any hydroxycar ^¬ boxylic acid. In this connection, a hydroxycarboxylic acid product can include any hydroxycarboxylic acid or combination of different hydroxycarboxylic acids. In one embodiment the hydroxycarboxylic acid is selected from the group of glycolic acid, 3- hydroxypropanoic acid, lactic acid, succinic acid, xy- loisosaccharine acid, anhydroisosaccharine acid, 3,4- dihydroxybutyric acid, 4-hydroxybutyric acid, glyceric acid, maleic acid, citric acid, oxalic acid and their combinations. Preferably, hydroxycarboxylic acid is selected from hydroxyl carboxylic acids formed from carbohydrate materials.

The hydroxycarboxylic acid can be formed by any method comprising a hydrolysis and fermentation stages. In one embodiment the hydrolysis can be select ^¬ ed from the group of acid hydrolysis, alkaline hydrol ^¬ ysis, enzymatic hydrolysis and their combinations. In one embodiment the hydrolysis and the fermentation may be carried by any method or process or apparatus known per se and suitable for the purpose can be used in hy ^¬ drolysis and fermentation.

In one embodiment, after the fermentation, and preferably before the hydroxycarboxylic acid separa ^¬ tion, the suspension containing the hydroxycarboxylic acid is filtered for separating fermentation residue and/or lignin from the suspension. The filtration device can be any filtration device known per se and suit- able for the purpose can be used in the filtration of the suspension. In one embodiment a residue of the fer ^¬ mentation can be treated by an anaerobic treatment, burning and/or lignin purification.

In one embodiment of the invention, the first separation stage 36a is accomplished by a separation process selected from the group of crystallization, evaporation, filtration, e.g. ultrafiltration and nano- filtration, electro-osmotic treatment, suspension melt crystallization and their combinations. In one embodi- ment the first separation stage is suspension melt crystallization, preferably water crystallization. In one embodiment, the first separation device 36a is selected from the group of evaporator, crystalli ^¬ zation device, filtration device, osmotic device, sus ^¬ pension melt crystallization device and their combina- tions. In one embodiment the first separation device is a suspension melt crystallization device. The first separation device can be any separation and/or concentration device known per se and suitable for the purpose can be used in the water separation and concentration of the hydroxycarboxylic acid composition.

In one embodiment of the invention, the se ^¬ cond separation stage 36b is accomplished by suspen ^¬ sion melt crystallization. Preferably, simultaneously hydroxycarboxylic acid is concentrated and purified. In one embodiment the second separation stage is hy ^¬ droxycarboxylic acid crystallization, e.g. lactic acid crystallization. In one embodiment, the second separa ^¬ tion device 36b is a suspension melt crystallization device, which can be any suspension melt crystallization device known per se and suitable for the purpose can be used in the separation of the hydroxycarboxylic acid and the concentration of the hydroxycarboxylic acid composition .

In one embodiment of the invention, at least a part of hydroxycarboxylic acid formed in the second separation stage is recirculated to the suspension be ^¬ tween the first and second separation stages. In one embodiment the apparatus comprises a recirculating means 39 for recirculating at least a part of the hydroxycar- boxylic acid 33 formed in the second separation device 36b to the suspension 32 placed between the first 36a and second 36b separation devices.

In one embodiment the separation process com ^¬ prises at least one intermediate stage between the first and second separation stages. In one embodiment the hy ^¬ droxycarboxylic acid is added into the intermediate stage. In one embodiment the separation comprises at least on pre-treatment stage before the first separation stage. In one embodiment the separation comprises at least one post-treatment stage after the second separa- tion stage.

In one embodiment, the concentrated hy- droxycarboxylic acid product 33 formed is used as such to have a desired product or is processed further to have a desired product. In one embodiment, the hy- droxycarboxylic acid procuct is used as a chemical, biochemical and/or polymer component.

By the method and apparatus of the invention, pure hydroxycarboxylic acid is provided with a good product yield. By the invention, it is possible to utilize different kinds of effluent which could not be utilized cost-effectively before to form valuable products. Further, products can be provided cost- effectively and with low production costs. EXAMPLES

In the following, the invention will be described in more detail by means of detailed exemplary embodiment with reference to the accompanying figures. In this example, the hydroxycarboxylic acid product is lactic acid.

Fig. 1 shows an apparatus for producing and separating lactic acid by the method according to the invention .

The apparatus of Fig. 1 includes an effluent feeding means 20 for feeding an effluent used as a raw stock 2 from a pulp mill 1. The effluent feeding means 20 comprises a pipe or a duct for transporting the ef ^¬ fluent. The effluent feeding means may also comprise pump(s) or any other equipment needed for feeding the effluent from the pulp mill to an ultrafiltration device 10. The apparatus includes an ultrafiltration device 10 for removing water 17 from the raw stock 2 and for concentrating the raw stock to provide a concentrate 3. Furthermore, the process includes a hydrolysis device 11 based on an acid hydrolysis or alkaline hydrolysis for hydrolyzing the concentrate 3 to form saccharides 4, and a fermentation device 12 for fermentating the saccharides 4 to form lactic acid. The apparatus includes a pH controlling means 18 a-c for controlling and adjusting the pH of the fermentation 12 by using a second efflu- ent 16 from the pulp mill 1. Before the hydrolysis 11 the concentrate 3 can be treated in a dwell tank 13, es ^¬ pecially if a bleaching filtrate is used as the second effluent. The second effluent can be fed in the dwell tank 13 and/or in the fermentation 12. The bacteria are mixed with the concentrate 3 in the hydrolysis step 11. The pH controlling means comprises at least one measur ^¬ ing device 18a for measuring the pH in the fermentation 12 and/or before the hydrolysis 11, a feeding device 18c for feeding the second effluent and a control unit 18b for controlling and adjusting the feeding of the second effluent on grounds of the pH measurements. The feeding device is pump or any other suitable equipment for feed ^¬ ing the second effluent from the pulp mill to the dwell tank 13 and/or the fermentation device 12. The control unit 18b contains reception means to receive signals from the measuring devices 18a, calculation means to form control signals, and control signal transmitting means to transmit the control signals formed in the con ^¬ trol unit to the feeding device 18c.

After the fermentation 12 a suspension 30 including lactic acid is led to a filtering device 35, where lignin and fermentation waste 38 is filtered from a fermentation mother suspension 31 including lactic acid.

The fermentation mother suspension 31 including lactic acid is concentrated in a two-stage concentration device 36a-b to form concentrated lactid acid 33. The apparatus of this invention comprises the two-stage con ^¬ centration device. The two-stage concentration device comprises a first suspension melt crystallization device 36a where water is removed from the fermentation mother suspension 31 including lactic acid and a second suspension melt crystallization device 36b where lactic acid 33 is separated from the fermentation mother suspension 32 from which water 37 has been removed for forming lac- tic acid 33 with concentration over 90 %. Water 37 from the first crystallization device 36a is led to the pulp mill 1. The residue fermentation mother suspension 34 is recirculated into the suspension 30 after the fermenta ^¬ tion 12. Further, the apparatus of the invention com- prises means 39 and 40 for adding lactic acid to the suspension 32 before the second crystallization device 36b to increase a concentration of the lactic acid in the second stage 36b. The recirculating means 39 recir ^¬ culates at least a part of the lactic acid 33 formed in the second crystallization device 36b to the suspen ^¬ sion 32 placed between the first 36a and second 36b crystallization devices.

In this example a suspension 30,31 containing lactic acid is formed from the pulp mill effluent 2 con- taining mainly bleaching filtrate by a hydrolysis 11, e.g. an entzymatic hydrolysis, and fermentation 12. In the hydrolysis the effluent is hydrolyzed to form sac ^¬ charides. In the fermentation the saccharides are fer ^¬ mented to form lactic acid. The suspension 30,31 con- taining lactic acid is led after the hydrolysis and fer ^¬ mentation to the lactic acid separation process 36a-b. Before the lactic acid separation the suspension 30 may be filtered, e.g. by an ultrafiltration device 35, for removing lignin and fermentation residue 38 from the suspension 31. Separated lignin and fermantion residue 38 can be further processed e.g. in anaerobic fermenta ^¬ tion, by burning or in lignin purification. The suspension 31 including lactic acid is concentrated by a crystallisation for forming a concentrated lactic acid. The lactic acid separation is based on two-stage crystallization which includes two stages 36a and 36b. The first stage 36a of the separation is water crystallization. The second stage 36b of the separation is lactic acid crystallization. In the first stage 36a water 37 is removed by crystallization from the suspension 31 to form a suspension 32 from which at least a part of water is removed. After the first stage 36a the suspension 32 contains about 30 % lactic acid. The sus ^¬ pension 32 is supplied to the second stage 36b of the separation. In the second stage 36b of the separation the lactic acid is concentrated and crystalllized from the suspension 32. Simultaneously it is purified. The lactic acid is thus recovered as pure lactic acid in solid form, not as a salt. After the second stage 36b the concentration of the lactic acid 33 is about 99 %. A residue 34 of the suspension 32 may be returned into the process or utilized in the other process. The separated lactic acid 33 can be used as a chemical, biochemical, polymer component or final product. A part of the sepa ^¬ rated lactic acid 33 is recirculated as a lactic acid flow by the recirculation means 39 to the suspension 32 to to increase a concentration of the lactic acid in the second stage 36b. Alternatively, pure lactic acid is added by the adding means 40 to the suspension 32 to to increase a concentration of the lactic acid in the se ^¬ cond stage 36b. Water 37 from the first stage 36a of the separation may be supplied to the pulp mill 1.

The method and the apparatus according to the invention are suitable as different embodiments to be used in the separation of most different hydroxycarbox- ylic acid products, e.g. lactic acid products.

The invention is not limited merely to the examples referred to above; instead, many variations are possible within the scope of the inventive idea defined by the claims.